Authority helps you authorize actions in your Rails app. It's ORM-neutral and has very little fancy syntax; just group your models under one or more Authorizer classes and write plain Ruby methods on them.

Role-based authorization system for Rails with a concise DSL for securing your Rails application. Acl9 makes it easy to get security right for your app, the access control code sits right in your controller, the syntax is very easy to understand, and acl9 makes it easy to test your access rules.

Ever needed to assign roles to a model, say a User, and build conditional behaviour on top of that? Enter RoleModel -- roles have never been easier! Just declare your roles and you are done. Assigned roles will be stored as a bitmask.

Simple role based security for restful_authentication
I am no longer involved in this project. If you are interested in becoming the new maintainer and making it your own, please contact me. I will no longer be responding to bug reports or questions.
Thanks,
Tim

Trust is a resource oriented framework for authorization control. It is compatible with Rails 3 and 4.
It has a loose coupling from the models, and features a native Ruby implementation language.
Support for inheritance and namespaced models as well as nested routes. Even permissions scheme supports inheritance.

Walruz provides an easy to use DSL to do composition of basic
authorization policies to create more complex ones, and then register
this composed policies on actions performed to the model begin accessed